Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$75.39	6.283%	$80.1268	$80.13	$80.15	$80.10
Purchase #2	$40.46	5.291%	$42.6007	$42.60	$42.60	$42.60
Purchase #3	$242.78	3.460%	$251.1802	$251.18	$251.20	$251.20
Purchase #4	$107.70	13.397%	$122.1286	$122.13	$122.15	$122.10
Purchase #5	$125.86	4.476%	$131.4935	$131.49	$131.50	$131.50
Purchase #6	$197.25	11.378%	$219.6931	$219.69	$219.70	$219.70
Purchase #7	$235.34	7.731%	$253.5341	$253.53	$253.55	$253.50
7 purchase totals =	$1,024.78		$1,100.7570	$1,100.75	$1,100.85	$1,100.70